The present invention relates to liquid spray injection and is a novel injector which is particularly suited to the research of high pressure injection processes of energetic liquid jets into high pressure reactive gas environments.
Gun technology is currently dominated by solid propellants. Nevertheless, it is becoming more and more apparent that liquid propellants have many advantages over solid propellants. Higher firing rates, greater automation and improved internal ballistic control are examples. New liquid propellants are also much cheaper than their equivalent solid propellants. Additionally, the logistics of liquid propellants are simpler and cheaper than that of solid propellants. The technology of guns using liquid propellants is, however, much more complex than guns using solid propellants. Still, significant progress has been achieved with Regenerative Liquid Propellant (RLP) guns. In these guns, the liquid propellant (normally a monopropellant) is stored in a reservoir outside the gun barrel, and a delivery and injection system is used to transfer the liquid propellant to the combustion chamber; this is where the complexity arises. Pumping equipment, which includes precise volume and pressure control, is readily available, but the state of the art in injectors is such that each specific application requires a new development effort. In RLP guns, the liquid injection is driven by the pressure in the combustion chamber itself via a differential area piston which amplifies the pressure in the liquid reservoir and thereby injects the liquid into the combustion chamber. Very high pressures are involved, anywhere from 2,000 psi to 60,000 psi. Considerable resources are currently committed to investigate the parameters controlling the injection process and to determine the requirements for optimum injector performance, which includes discharge coefficients (mass flow rates for given injection pressures) and liquid jet breakup (spray) in the combustion chamber.
With the exception of the injectors used in RLP guns, prior art injectors derive their injection pressure from sources other than the existing combustion chamber pressure. For example, such sources include pumps and external hydraulic systems which restrict these injectors to low mass flow rates and typically limiting the jets to diameters of less than 1 mm and velocities of less than 120 m/sec, with injection pressures that seldom exceed 5,000 psi. The liquid reservoirs, prior to the initiation of injection, are either exposed to the combustion chamber environment (with the risk of the liquid being ignited catastrophically in the reservoir in the case of monopropellants) or sealed from it by a check valve arrangement, in which case the injection port area fluctuates with the injection pressure, thus perturbing uncontrollably the jet and increasing the risk of liquid ignition in the injection port passage and flame flashback into the liquid reservoir. The RLP gun injector utilizes only the combustion chamber pressure and it is preset to start injection at a particular combustion chamber pressure. It cannot be set (without mechanical modifications) to initiate injection at arbitrary combustion chamber pressures and once injection starts, the injection pressure is solely determined by the geometry of the injector and the combustion chamber pressure. Also, no injection can take place in the absence of significant combustion chamber pressure.
RLP gun injectors can successfully inject jets having annular geometries, but they are not well suited to inject full core jets since in the later geometry it does not provide for pre-injection insulation of the liquid reservoir from the combustion chamber. When research is conducted in this area, it is highly advantageous to inject full core jets since this geometry is more amenable for diagnostics and more easily modeled analytically. The injector described in the present invention utilizes one aspect of operation from the RLP gun injector and is thus capable of high pressure and high mass flow injections; it does not, however, have the limitation of the RLP gun injector and is more versatile and safe (with energetic propellants) than any other known injector.